Now, a freshly signed deal will help keep it that way, county officials said.

The Board of Supervisors last week signed off on an agreement with the Nature Conservancy to bring in a $240,000 grant to help support the Ring Mountain Stewardship and Habitat Restoration Program through early 2021. The program is now several years in and has done much to revive and highlight the rare natural resources on the 387-acre preserve that straddles the boundary between Corte Madera and Tiburon.

“We have amazing rare plants, interesting geology and great community involvement that have worked to really improve the preserve,” said Andy Longman, Ring Mountain’s stewardship coordinator, as he enthusiastically showed off the area Monday. “It’s a great mix here.”

Ring Mountain provides an opportunity to see rare wildflowers, a Native American grinding stone and a rock with prehistoric petroglyphs, among other sites. The Coast Miwoks once inhabited the region.

The preserve is named for George Ring, a Marin County supervisor from 1895 to 1903.

Serpentine is a mineral that creates difficult growing conditions for plants in the preserve’s soils, Longman noted. That has produced some rare species of plants, including the Tiburon mariposa lily, which grows nowhere else in the world.

All of the preserve was almost lost.

The area was once slated for development, but Phyllis Ellman, a Tiburon resident, rallied an effort to save Ring Mountain from housing. Known as “Mother Botany” for her knowledge of local wildflowers, Ellman helped preserve Ring Mountain in the late 1970s.

The Nature Conservancy eventually acquired the land in the 1980s and then turned it over to the county in 1995.

Over the years invasive plants sprung up, which threatened the rare plant species.

In 2011, the county began working with the Nature Conservancy to better protect the preserve and rid it of damaging invaders. Since then there have been 189 volunteer events and 6,000 hours of labor poured in by 3,500 volunteers. Students from Marin Country Day School, Cove School, New Village School, Marin Academy and others have worked on the mountain and removed invasives to help it heal.